To retrieve the IDs of all RequiredFieldValidator controls in a web form page from the code-behind file, you can use the following steps:

1. Ensure that you have added the RequiredFieldValidator controls to your web form in the markup file (e.g., ASPX file) and have assigned unique IDs to each validator.
2. In the code-behind file (e.g., the .cs file for C# or .vb file for VB.NET), import the necessary namespaces at the top of the file if they are not already present:

   using System;
   using System.Web.UI.WebControls;

3. Inside the appropriate method or event handler in the code-behind file, use the FindControl method to locate the RequiredFieldValidator controls by their IDs. You can iterate through the Controls collection of the form or any specific container (e.g., Panel, ContentPlaceHolder) to find the validators recursively:

   protected void Page_Load(object sender, EventArgs e)
   {
       // Initialize a list or array to store the validator IDs
       List<string> validatorIDs = new List<string>();

       // Find validators recursively within the form or a specific container
       FindValidatorsRecursive(Page.Controls, validatorIDs);

       // Now you have the list of validator IDs
       foreach (string validatorID in validatorIDs)
       {
           // Do something with the validator ID
           // For example, you can add them to a collection or output them
           Console.WriteLine(validatorID);
       }
   }

   private void FindValidatorsRecursive(ControlCollection controls, List<string> validatorIDs)
   {
       foreach (Control control in controls)
       {
           if (control is RequiredFieldValidator)
           {
               RequiredFieldValidator validator = (RequiredFieldValidator)control;
               validatorIDs.Add(validator.ID);
           }

           if (control.HasControls())
           {
               FindValidatorsRecursive(control.Controls, validatorIDs);
           }
       }
   }

The FindValidatorsRecursive method takes two parameters: ControlCollection and List<string>. It recursively searches for controls within the specified ControlCollection and adds the IDs of any RequiredFieldValidator controls it finds to the validatorIDs list.

4. Depending on your requirements, you can modify the code to store the validator IDs in a different data structure or perform additional actions with the IDs as needed.

Note that in the above example, I assumed you are using C# as the programming language. If you are using VB.NET, the code will be slightly different, but the overall approach remains the same.